Nursery: feeding, changing, looking after children.
Nanny: as above, plus: shopping, cooking, meal planning, laundry, organising playdates, tumbletots, monkey music.
It's not rocket science, but if she's a sweetheart who would happily sit inside all day and play nicely with your dd, then she's not a nanny. On the other hand, if you think she has the organisational skills to sort the above, the nouse to realise it's a bad idea to book a term's worth of classes at nap time (for example,) capable of providing nutritious food, shows initiative and can cope with the autonomy etc then hire her.
There are many posts like the one I mentioned before - those that say 'the children adore her but...[problem with nursery duties/meeting other nannies and children/being able to cook]' None of which is insurmountable of course, it just depends on how much training you want to be doing intitially.
Bink's right too - in many ways nannying is not for shy-and-retiring types. I'm trying to think of a good analogy, but the only thing I can come up with is the difference between being a shepherd's job of a) rounding up a flock of sheep versus b) one to one care of a sheepdog!
Also be aware there is a power shift. As a nursery worker, her boss was her manager, not the parents, and the nursery provided a service. Now, she has to do what you tell her, to be blunt!
I seem to be painting a very bleak picture here - for all we know she might be climbing the walls in the nursery and desperate to have a less boring job (for her.) She may well be a super nanny, but you are right in thinking there will be a few things to be aware of first.